Isomerization of epoxyalkenes to 2,5-dihydrofurans

ABSTRACT

Disclosed are processes for the isomerization of epoxyalkenes to dihydrofurans by contacting an epoxyalkene with a catalyst comprising a quaternary organic onium iodide compounds, optionally deposited on a non-acidic support and/or in combination with a Lewis acid co-catalyst. The catalyst may comprise a supported catalyst, an unsupported catalyst or a solution of the catalytically-active components in an inert, organic solvent.

This application is a continuation-in-part of application Ser. No. 07/490,208 filed Mar. 8, 1990, now abandoned.

This invention pertains to isomerization processes and, more particularly, to processes whereby γ,δ-epoxyalkenes and γ,δ-epoxycycloalkenes are isomerized to obtain the corresponding 2,5-dihydrofuran compounds. This invention also pertains to novel catalyst systems useful in the described isomerization processes and to methods for the preparation of supported catalyst systems.

Dihydrofurans are reactive heterocyclic species which are useful in a variety of applications, e.g., as intermediates in the production of useful polymers and chemicals. However, the use of dihydrofurans for such purposes has heretofore been restricted due to the non-availability of cost-effective preparative procedures therefor.

In addition, dihydrofurans are readily reduced to produce the corresponding tetrahydrofuran species, which are also useful in a variety of applications, e.g., as polar aprotic reaction solvents, co-solvents, reactive intermediates in the production of useful polymers, copolymers, and the like.

U.S. Pat. Nos. 3,932,468 and 3,996,248 disclose the production of 2,5-dihydrofurans by the rearrangement of substituted or unsubstituted epoxyalkenes with a homogeneous catalyst system comprising hydrogen iodide or hydrogen bromide and a transition metal Lewis acid in an organic solvent. This process suffers from a number of disadvantages including the use of corrosive hydrogen halides, the need for expensive, high-boiling tertiary amide solvents, e.g., N-methyl-2-pyrrolidinone, to dissolve the transition metal Lewis acid. We have found that the process of U.S. Pat. Nos. 3,932,468 and 3,996,248 also results in the unwanted production of up to 15% α,β-unsaturated aldehydes or ketones.

The thermal (i.e., non-catalytic) rearrangement of 3,4-epoxy-1-butene has been studied and shown by Crawford et al in the Canadian Journal of Chemistry, Vol. 54, pages 3364-3376 (1976) to produce a variety of products, including 2,3-dihydrofuran, cis and trans 2-butenal and 3-butenal.

Other reactions of epoxides have been reported. See, for example, U.S. Pat. No. 4,600,800, where epoxides are converted to allylic alcohols by contacting an epoxide in the liquid phase with solid alumina catalysts.

Another example of the rearrangement of epoxides is described in the Journal of Organometallic Chemistry, Vol. 359, pages 255-266 (1989), wherein Sato et al report the formation of α,β-unsaturated aldehydes and ketones by the rhodium (I) catalyzed isomerization of 1,3-diene monoepoxides.

U.S Pat. No. 4,897,498 describes an efficient process for the preparation of γ,δ-epoxyalkenes by the selective monoepoxidation of dienes. Thus, a process is needed for the conversion of such epoxyalkenes to dihydrofurans in satisfactory selectivity and/or yields wherein the product may be readily recovered from the catalyst and the catalyst reused and used in continuous operation.

In accordance with the present invention, we have discovered a catalytic process for the isomerization of γ,δ-epoxyalkenes to produce dihydrofurans. The process provides high levels of epoxyalkene conversion with high selectivity to the desired dihydrofuran product. Long catalyst lifetimes are realized and the product may be recovered by relatively simple means since the catalyst and reaction mixture are readily separated by such simple techniques as distillation, decantation, filtration, gas stripping methods, gas/liquid flow separation, and the like.

Our invention also provides novel catalyst systems, both supported and unsupported, which are useful, for example, to promote the isomerization of epoxyalkenes to dihydrofurans. Processes for preparing the supported catalyst systems are also provided herein.

In accordance with the present invention, there is provided a process for the isomerization of γ,δ-epoxyalkenes to the corresponding 2,5-dihydrofuran compounds, which process comprises contacting a γ,δ-epoxyalkene or γ,δ-epoxycycloalkene with a catalytic amount of a quaternary organic onium iodide, e.g., a compound consisting of an ammonium, phosphonium or arsonium cation and an iodide anion, under isomerization conditions of temperature and pressure.

The γ,δ-epoxyalkene and γ,δ-epoxycycloalkene reactants may contain from 4 to about 20 carbon atoms, preferably from 4 to about 8 carbon atoms. Examples of the epoxyalkene and epoxycycloalkene reactants include compounds having the structural formula: ##STR1## wherein each R¹ is independently selected from hydrogen, alkyl of up to about 8 carbon atoms, a carbocyclic or heterocyclic aryl group of about 5 to 10 carbon atoms or halogen or any two R¹ substituents collectively may represent an alkylene group forming a ring, e.g., alkylene containing in the main chain up to about 8 carbon atoms. The preferred epoxyalkene reactants comprise compounds of formula (I) wherein only two of the R¹ substituents individually may represent lower alkyl, e.g., alkyl of up to about 8 carbon atoms, or collectively represent straight or branched chain alkylene of up to about 8 carbon atoms. Exemplary compounds contemplated for use in the practice of the present invention include 3,4-epoxy-3-methyl-1-butene, 2,3-dimethyl-3,4-epoxy-1-butene, 3,4-epoxycyclooctene, 3,4-epoxy-1-butene, 2,5-dimethyl-2,4-hexadiene monoepoxide, and the like. The epoxyalkene reactant of primary interest is 3,4-epoxy-1-butene.

The 2,5-dihydrofuran compounds obtained in accordance with our novel process have the structural formula: ##STR2## wherein the R¹ substituents are defined above. Of the compounds which may be obtained in accordance with our invention, the most important is 2,5-dihydrofuran.

The quaternary onium iodide compounds which may be used as the catalyst in our novel process are known compounds and/or may be prepared according to published procedures. See, for example, U.S. Pat. No. 3,992,432 and the references cited therein. Exemplary quaternary organic onium iodide compounds include mono-, di-, tri-, or tetra-substituted quaternary onium iodides, wherein said substituents are selected from hydrogen, alkyl or substituted alkyl groups, cycloalkyl or substituted cycloalkyl groups, carbocyclic aryl or substituted carbocyclic aryl groups, heteroaryl or substituted heteroaryl groups, ferrocenyl, wherein each of said substituents may be bonded to one another to form a cyclic, heterocyclic, polycyclic or poly-heterocyclic structure. When used on a support or as a melt, the onium compounds normally contain at least 6 carbon atoms, preferably at least 12 carbon atoms, and have melting points not greater than about 225° C., preferably not greater than about 200° C.

Examples of the onium iodide catalysts are compounds conforming to the formulas ##STR3## wherein each R² independently is selected from hydrogen, alkyl or substituted alkyl moieties having up to about 20 carbon atoms, cycloalkyl or substituted cycloalkyl having about 5 to 20 carbon atoms, or aryl or substituted aryl having about 6 to 20 carbon atoms; or when Y is P, each R² also may be selected from alkoxy of up to about 20 carbon atoms, cycloalkoxy of about 5 to 20 carbon atoms, aryloxy of 6 to 10 carbon atoms or halogen;

two or three R² substituents collectively may represent joined hydrocarbylene groups, e.g. alkylene having 4 to 6 main chain carbon atoms or unsaturated groups such as --CH═CHCH═CHCH═ and lower alkyl substituted alkylene and unsaturated groups, which form a mono- or poly-cyclic ring with the Y atom to which they are bonded;

each R³ is independently selected from hydrocarbylene moieties or substituted hydrocarbylene moieties;

x is 0 or 1, and

Y is N, P or As; provided that the quaternary onium iodide compound contains at least 6 carbon atoms. The substituted groups and moieties referred to above bear one or more substituents such as groups having the formulas ##STR4## wherein each R⁴ is independently selected from hydrogen or alkyl of up to about 20 carbon atoms and X is halogen. As used herein, the terms "hydrocarbylene moieties" refers to alkylene moieties having up to about 6 carbon atoms, arylene or polyarylene moieties having 6 to 20 carbon atoms.

The preferred onium iodide catalysts are the quaternary ammonium and quaternary phosphonium iodide compounds. Exemplary ammonium compounds include tetrapentylammonium iodide, tetrahexylammonium iodide, tetraoctylammonium iodide, tetradecylammonium iodide, tetradodecylammonium iodide, tetrapropylammonium iodide, tetrabutylammonium iodide, monooctylammonium iodide, dioctylammonium iodide, trioctylammonium iodide, N-octylquinuclidinium iodide, N,N'-dimethyl-N,N'-dihexadecylpiperazinium diiodide, dimethylhexadecyl-[3-pyrrolidinylpropyl]ammonium iodide, N,N,N,N',N',N'-hexa(dodecyl)octane-1,8-diammonium diiodide, N,N,N,N',N',N'-hexa(dodecyl)butane-1,4-diammonium diiodide, N-octylpyridinium iodide, and the like.

Exemplary phosphonium compounds include tetraoctylphosphonium iodide, tetrabutylphosphonium iodide, triphenyl(hexyl)phosphonium iodide, triphenyl(octyl)phosphonium iodide, tribenzyl(octyl)phosphonium iodide, tribenzyl(dodecyl)phosphonium iodide, triphenyl(decyl)phosphonium iodide, triphenyl(dodecyl)phosphonium iodide, tetrakis(2-methylpropyl)phosphonium iodide, tris(2-methylpropyl)(butyl)phosphonium iodide, triphenyl(3,3-dimethylbutyl)phosphonium iodide, triphenyl(3-methylbutyl)phosphonium iodide, tris(2-methylbutyl)(3-methylbutyl)phosphonium iodide, triphenyl[2-trimethylsilylethyl]phosphonium iodide, tris(p-chlorophenyl)(dodecyl)phosphonium iodide, hexyltris(2,4,6-trimethylphenyl)phosphonium iodide, tetradecyltris(2,4,6-trimethylphenyl)phosphonium iodide, dodecyltris(2,4,6-trimethylphenyl)phosphonium iodide, and the like.

Tetra-substituted ammonium and phosphonium iodide compounds containing a total of about 16 to 60 carbon atoms are especially preferred. Such compounds have the formulas ##STR5## wherein each R⁵ substituent independently is selected from alkyl of up to about 20 carbon atoms and each R⁶ substituent is independently selected from R⁵, benzyl, phenyl or phenyl substituted with up to 3 substituents selected from lower alkyl (alkyl of up to about 4 carbon atoms) lower alkoxy or halogen; or

two R⁵ substituents collectively may represent alkylene of 4 to 6 carbon atoms including alkylene of 4 to 6 carbon atoms substituted with lower alkyl; provided, as specified above, that the quaternary iodide compounds contain about 16 to 60 carbon atoms.

Another group of preferred ammonium iodide compounds are comprised of N-alkyl-azabicycloalkane and N-alkyl- and N,N'-dialkyl-diazabicycloalkane iodide compounds containing 6 to about 12 ring carbon atoms, e.g., bicyclic compounds having the general formula ##STR6## wherein R⁵ is defined above and A is the residue of an azabicycloalkane or diazabicycloalkane having 6 to 12 ring carbon atoms (including the 2 carbon atoms in the above general formula), e.g., azabicyclooctane, azabicyclononane, diazabicyclooctane and the like.

The onium iodide compounds described hereinabove may be employed in combination with a Lewis acid to catalyze the isomerization process of our invention. Examples of such optional Lewis acid co-catalysts include the alkali metal halides, zinc halides, magnesium halides, tin (II) halides, tin (IV) halides, titanium (IV) halides, titanium (IV) tetra-lower-alkoxides, zirconium (IV) halides, manganese (II) halides, iron (III) halides, or iron (III) acetylacetonate. Preferably, the Lewis acid co-catalyst is an alkali metal iodide, zinc iodide, zinc chloride, magnesium iodide, tin (II) iodide, tin (IV) iodide, titanium (IV) iodide, titanium (IV) tetramethoxide, titanium (IV) tetraethoxide, titanium (IV) tetraisopropoxide, zirconium (IV) iodide, manganese (II) iodide, manganese (II) chloride, iron (III) iodide, iron (III) acetylacetonate or a combination thereof. The Lewis acid co-catalysts which are particularly preferred are polarizable iodides, such as, for example, titanium (IV) iodide, zirconium (IV) iodide, and, especially, zinc iodide and tin (II) iodide.

The Lewis acid co-catalyst alternatively may be selected from organotin (IV) and organoantimony (V) compounds such as hydrocarbyltin trihalides, dihydro. carbyltin dihalides, trihydrocarbyltin halides, tetrahydrocarbyltin compounds and tetrahydrocarbylantimony halides. Examples of such organometallic compounds include compounds having the formula

    (R.sup.7).sub.n --Sn--Hal.sub.(4-n) and (R.sup.7).sub.4 --Sb--Hal

wherein

each R⁷ independently is selected from alkyl or substituted alkyl moieties having up to about 20 carbon atoms, cycloalkyl or substituted cycloalkyl having about 5 to 20 carbon atoms, carbocyclic aryl or substituted carbocyclic aryl having about 6 to 20 carbon atoms, or heteroaryl or substituted heteroaryl moieties having about 4 up to 20 carbon atoms;

Hal is a halogen atom such as bromo or, preferably, iodo; and

n is 1, 2, 3 or 4.

Examples of organometallic compounds include dibutyltin diiodide, tributyltin iodide, trioctyltin iodide, triphenyltin iodide, tributyltin bromide, trimethyltin iodide, butyltin triiodide, tetrabutyltin, tetraoctyltin, triphenyltin iodide, tribenzyltin iodide, dimethyltin diiodide, diphenyltin diiodide, triphenyltin bromide and tetraphenylantimony iodide.

The preferred organometallic compounds comprise tin (IV) iodides having the above general formula and a total carbon content of about 3 to 24 carbon atoms wherein

each R⁷ substituent independently is selected from alkyl of up to about 12 carbon atoms, benzyl, phenyl or phenyl substituted with up to 3 substituents selected from lower alkyl, lower alkoxy or halogen;

Hal is iodo; and

n is 2 or 3.

The quaternary organic onium iodide catalyst, or the quaternary organic onium iodide-Lewis acid catalyst system, may be employed in the process provided by this invention in either a supported or unsupported form. The supported catalysts of this invention comprise an essentially non-acidic catalyst support material having one or more quaternary organic onium iodide compounds distributed on the surface thereof as a substantially continuous and uniform film and, optionally, one or more of the Lewis acids described above, e.g., an alkali metal halide, zinc halide, magnesium halide, tin (II) halide, tin (IV) halide, titanium (IV) halide, titanium (IV) lower alkyl alkoxide, organotitanium (IV) halide, zirconium (IV) halide, manganese (II) halide, iron (III) halide, iron (III) acetylacetonate or one of the organotin compounds or organoantimony halides described hereinabove.

The essentially non-acidic support may be in the form of a powder or shaped material having sufficient structural integrity to allow passage of gaseous reactant through a packed or fluidized bed of the supported catalyst under reaction conditions. Preferred support materials employed in the practice of the present invention are materials having a particle size in the range of about 20 up to 200 microns and having a crush strength of at least about two pounds. Support materials having crush strengths of at least ten pounds are especially preferred.

A variety of shapes are suitable for use as the support material employed in the practice of the present invention. For example, pellets, spheres, rings, saddles, extruded cylinders, and the like can be employed, so long as such materials have dimensions and packing characteristics so as to allow for the ready passage of gaseous reactant and product through a packed or fluidized bed of the catalyst under reaction conditions.

Examples of the materials which may be employed as the support include zinc oxide, zinc carbonate, magnesium oxide, silica, alumina, titanium oxide, lanthanum oxide, boron nitride, boron carbide, silicon nitride, silicon carbide, tin oxide, calcium oxide, barium oxide, strontium oxide, zirconium oxide, carbon, boron phosphate, or zirconium phosphate, as well as mixtures of any two or more thereof. The preferred support materials contemplated for use in the practice of the present invention include zinc oxide, zinc carbonate, magnesium oxide, silica, alumina, titanium oxide, boron nitride, silicon nitride, silicon carbide, calcium oxide, barium oxide and carbon as well as mixtures of any two or more thereof. Silica, alumina, titanium oxide and zinc oxide are particularly preferred support materials.

The amount of the quaternary organic onium iodide component of the novel catalyst compositions of this invention can vary substantially depending, for example, on the particular support material and the form, e.g., surface area, thereof, the mode in which the isomerization process is operated, the particular quaternary onium iodide present, the presence or absence of a Lewis acid co-catalyst, etc. The amount of the onium iodide, calculated as weight iodide, typically will be in the range of about 0.1 to 30 weight percent based on the total weight of the catalyst. Preferred loading levels fall in the range of about 0.5 up to 20 weight percent (same basis).

When present, the quantity of Lewis acid component of the catalyst compositions generally is in the range of about 0.01 to 30 weight percent, based on the total weight of the catalyst. The preferred quantity of the inorganic Lewis acid co-catalysts, e.g., titanium (IV) iodide, zirconium (IV) iodide, zinc iodide and tin (II) iodide, is in the range of about 0.02 up to 5.0 weight percent based on the total weight of the catalyst.

Another embodiment of the catalyst compositions provided by our invention comprise a support material having deposited thereon (i) about 0.1 to 30 weight percent of an organic onium iodide and (ii) about 0.01 to 30 weight percent of an organotin (IV) compound or organoantimony (V) halide, based on the total weight of the catalyst composition. These catalyst compositions preferably comprise:

(i) about 0.5 to 20 weight percent of a tetra-substituted ammonium and/or phosphonium iodide compound of formula (VII) and/or (VIII); and

(ii) about 0.02 to 20 weight percent of an organotin iodide containing a total of about 3 to 24 carbon atoms and having the formula

    (R.sup.7).sub.n --Sn--I.sub.(4-n)

wherein

each R⁷ substituent independently is selected from alkyl of up to about 12 carbon atoms, benzyl, phenyl or phenyl substituted with up to 3 substituents selected from lower alkyl, lower alkoxy or halogen; and

n is 2 or 3; on (iii) a support material selected from silica, alumina, zinc oxide, titanium oxide, boron nitride and silicon carbide.

The supported catalysts described herein may be prepared by a variety of procedures as will be readily apparent to those skilled in the art. For example, the supported catalysts may be prepared by the steps comprising:

(a) impregnating a suitable support with a solution of one or more quaternary organic onium iodide compound and, optionally, one or more Lewis acids, and thereafter

(b) removing the solvent from the impregnated support.

Solvents contemplated for use in the impregnation step include polar solvents capable of substantially dissolving the quaternary organic onium iodide and the optionally employed Lewis acid. Such solvents include water, lower alcohols such as methanol, ethanol, isopropyl alcohol, and the like. Preferred solvents are those which can be easily removed by standard evaporative techniques once the desired impregnation has been carried out.

The volume of solvent required is 0.5 to 20.0 ml of solvent (plus quaternary organic onium iodide and, optional Lewis acid) per gram of support, the minimum volume of solvent being defined as that volume required to cover the catalyst support. The support and impregnation solution are agitated (typically by rotary tumbling) for 0.2 to 2.0 hrs at slightly elevated temperatures, e.g., 20° to 60° C., to maximize interaction of support and catalytic components. The solvent is preferentially removed by rotary evaporation at reduced pressure at temperatures ranging from 40° to 100° C., or alternatively by drying in a heated forced air oven, or further alternatively by spray-drying the catalyst solution on the support. After drying, the catalyst is ready to be loaded into a reactor.

Prior to contacting the catalyst with an epoxyalkene under isomerization conditions, the catalyst optionally may be subjected to pre-treatment conditions of time and temperature sufficient to activate said catalyst relative to non-pretreated catalyst. Typical pre-treatment conditions of time and temperature comprise a temperature at least as high as the melting point of said quaternary organic onium iodide, but no greater than 225° C., for a time in the range of about 0.1 up to 10 hours.

The conditions of temperature and pressure and the space velocity employed in our novel isomerization process can vary considerably depending on various factors such as the activity of the catalyst used, the degree of conversion and/or selectivity desired, the gas hour space velocity employed, the mode of operation and the like. For example, the process may be carried out at a temperature in the range of about 60° to 225° C. although temperatures of about 100° to 200° C. are more typical. The total reaction pressure may be in the range of about 1.02 to 70 bar (absolute) with the preferred range being about 1.1 to 20 bar total pressure.

The gas hourly space velocity may be varied substantially, e.g., from about 1 to about 10,000, although our process normally is performed using gas hourly space velocities in the range of about 10 up to 5,000 (hr⁻¹). The epoxyalkene reactant may constitute up to 100% of the feed composition or may be fed along with an inert diluent wherein volume ratio of the epoxyalkene:inert diluent can vary over a wide range of values, typically within 1:100 to 4:1. Exemplary inert gas diluents include helium, argon, nitrogen, carbon dioxide, or hydrocarbons which are gaseous under reaction conditions. Preferably, the epoxyalkene concentration is in the range of about 5 up to 80 volume percent of the feed composition.

The isomerization process may be carried out using the catalysts described herein either in a supported or unsupported form. Thus, the supported catalysts may be utilized in fixed or fluidized beds using reactor configurations well-known to those skilled in the art.

When the catalyst is unsupported, it can be used at temperatures either below, at or above the melting point of the quaternary organic onium iodide salt. When the catalyst is at or above its melting point and exists as a substantially liquid phase, it is necessary to maintain the catalyst in a reactor volume such that the passage of the gaseous feed and product molecules is not restricted, yet contains the catalyst in the reactor volume. An up-flow reactor is suitable for this purpose since the gaseous feed maintains the catalyst in the appropriate position in the reactor, yet permits the passage of unreacted feed and reaction products through the liquid, or substantially liquid, phase catalyst and into the downstream refining/recycle apparatus. In an especially preferred mode of operation, the catalyst is in a vessel with a closed bottom and the feed is added through a gas dispersion apparatus below the level of the catalyst. The unreacted feed and reaction products can exit from the top of the reactor.

The unsupported catalyst system preferably is used in our process as a melt of an intimate mixture of one or more of the quaternary onium iodide compounds and, optionally, one or more of the Lewis acid co-catalysts described hereinabove. The onium iodide:co-catalyst weight ratio of the unsupported catalyst system can vary substantially, e.g. from 500:1 to 1:100, depending on the particular co-catalyst selected. The preferred onium iodide:co-catalyst weight ratios depend on whether the co-catalyst is (1) an organotin (IV) compound or an organoantimony (V) halide or (2) one of the other Lewis acids described herein above. Thus, for the unsupported catalyst systems containing an inorganic Lewis acid, such as titanium (IV) iodide, zirconium (IV) iodide, zinc iodide and tin (II) iodide, the preferred onium iodide:co-catalyst weight ratio is about 200:1 to 5:1 and for the organotin (IV) compounds and organoantimony (V) halides the preferred onium iodide:co-catalyst weight ratio is about 1:100 to 50:1. Particularly preferred unsupported catalyst systems comprise a mixture of one or more of the tetra-substituted ammonium or phosphonium iodide compounds described hereinabove and tin (II) iodide, zinc iodide or an organotin iodide.

The unsupported quaternary organic onium iodide and/or Lewis acid catalyst may be used with an inert organic solvent if desired to alter the reaction conditions and/or reactor configuration. The optional, inert organic solvent may be used, for example, to change the concentration of the quaternary organic onium iodide and/or the Lewis acid or to assist in heat and/or mass transfer characteristics of the catalytic process.

Thus, another embodiment of our invention comprises the isomerization of an epoxyalkene to the corresponding 2,5-dihydrofuran in the presence of a homogeneous catalyst solution. This embodiment may be carried out in the presence of one or more of the above-described organometallic compounds although reaction rates are relatively slow if an organic onium iodide is not included. Accordingly, the homogeneous catalyst solution preferably comprises a catalytic amount of (i) one or more of the above-described organometallic compounds and (ii) one or more of the above-described organic onium iodides in (iii) an inert organic solvent, i.e., a solvent which does not react with the γ,δ-epoxyalkene or γ,δ-epoxycycloalkene reactants or the 2,5.dihydrofuran products. Examples of the solvents which may be used include aliphatic and aromatic hydrocarbons such as heptane, toluene, specific or mixed xylenes, pseudocumene, and mesitylene; halogenated hydrocarbons such as chlorobenzene, 1,2-dichlorobenzene, and 1,1,2,2-tetrachloroethane; ketones such as cyclohexanone, 5-methyl-2-hexanone, and 2-heptanone; ethers such as 2,5-dihydrofuran, tetrahydrofuran, and bis(2-methoxyethyl)ether; esters such as isobutyl acetate; and tertiary amides such as N-methyl-2-pyrrolidinone, N-cyclohexyl-2-pyrrolidinone, N-ethyl-2-pyrrolidinone, and N,N-dimethylacetamide. Normally, for ease of separation, the solvent or mixture of solvents employed have boiling points at least 20° C. above the boiling point of the 2,5-dihydrofuran product and the unsaturated aldehyde or ketone by-products.

The concentrations of the organometallic compound and the optional onium iodide in the inert, organic solvent can be varied substantially depending, for example, on the particular catalytically-effective components present, the design of the reactor system, etc. Typically, the concentration of the organometallic compound will be about 1 to 50 weight percent and the concentration of the onium iodide compound, when present, will be about 1 to 70 weight percent, both concentrations being based on the total weight of the catalyst solution. Normally, the mole ratio of onium iodide to organometallic compound is at least 1:1.

The preferred catalyst solutions comprise

(i) about 1 to 25 weight percent of an organotin iodide containing about a total of about 3 to 24 carbon atoms and having the formula

    (R.sup.7).sub.n --Sn--I.sub.(4-n)

wherein

each R⁷ substituent independently is selected from alkyl of up to about 8 carbon atoms, benzyl, phenyl or phenyl substituted with up to 3 substituents selected from lower alkyl, lower alkoxy or halogen; and

n is 1, 2, 3 or 4; and

(ii) about 1 to 25 weight percent of a tetrasubstituted ammonium or phosphonium iodide of formula (VII) and/or (VIII); and

(iii) an inert organic solvent selected from hydrocarbons and chlorinated hydrocarbons having up to about 10 carbon atoms.

Toluene, mixed or specific xylene isomers, chlorobenzene, mixed or specific dichlorobenzene isomers, pseudocumene, and mesitylene are particularly preferred solvents.

The isomerization process may be carried out in the liquid phase using the catalyst solutions described hereinabove by contacting a γ,δ-epoxyalkene or γ,δ-epoxycycloalkene at a temperature of about 50° to 200° C., preferably about 100° to 150° C., depending on the solvent or mixture of solvents employed. The process may be carried out at atmospheric or super-atmospheric pressures, e.g., up to about 22 bar (absolute).

The process employing the catalyst solution may be carried out in a batch, semi-continuous or continuous mode of operation. For example, batch operation may comprise refluxing a mixture of the γ,δ-epoxyalkene and catalysts, e.g. tributyltin iodide and tetraheptyl ammonium iodide, in a solvent such as p-xylene for a time sufficient to convert essentially all the epoxide to the 2,5-dihydrofuran. The products are then separated by distillation from the mixture. The undistilled catalyst solution may be reused in a subsequent reaction.

The catalyst solution preferably is employed in a continuous mode of operation wherein a γ,δ-epoxyalkene or γ,δ-epoxycycloalkene is added to a recirculated catalyst solution which is then introduced into a continuous reactor. After isomerization, the reaction stream is fed to a distillation system for removal of product or products and recycle of the catalyst solution. Examples of continuous reactor designs in which the process can be performed are continuous stirred tank reactors and plug flow reactors.

Our novel isomerization process and the catalyst systems, compositions and solutions useful in practicing the process are further illustrated by the following examples.

PREPARATION OF CATALYSTS EXAMPLE 1

Tetrabutylammonium iodide (1.786 g) was dissolved at 25° C. in ethyl alcohol (80 mL) in a 250 mL, round bottom flask. Zinc oxide (5.0 g, ultrapure) powder was added and the mixture was agitated for twenty minutes at 40° C. on a rotary evaporator. The zinc oxide used had a surface area of 3.8 square meters per g (m² /g) and a particle diameter in the range of 75 to 150 microns. The alcohol was then removed on the rotary evaporator at 40° C. under vacuum. The supported catalyst obtained contained 18.2 weight percent tetrabutylammonium iodide.

EXAMPLE 2

Tetradodecylammonium iodide (51.24 g), zinc iodide (1.06 g) and ethyl alcohol (200 mL) were placed in a one-liter, fluted flask and placed on a rotary evaporator and agitated for five minutes in a 60° C. bath. Silica extrusions (400 g, Calsicat SiO₂ pellets, 3/16" diameter having a surface area of approximately 0.5 m² /g and a general composition of 100% SiO₂) were then added and agitation continued for twenty minutes in the bath at 60° C. The alcohol was then removed on the rotary evaporator at 60° C. under vacuum. The supported catalyst obtained contained 11 weight percent tetradodecylammonium iodide and 0.23 weight percent zinc iodide.

EXAMPLE 3

Triphenyl(hexyl)phosphonium iodide (0.250 g) and zinc iodide (0.0050 g) were placed in a 50.mL flask and then silica (2.0 g) was added. The silica support material was prepared by grinding the silica extrudate described in Example 2 and classifying the ground material and using the portion which passed a 10 mesh sieve and was retained on a 20 mesh. The flask was placed on a rotary evaporator and agitated for 20 minutes with the flask in the bath at 60° C. Methanol was removed while the flask was in the 60° C. bath using vacuum. The supported catalyst obtained (2.25 g) contained 11 weight percent triphenyl(hexyl)phosphonium iodide and 0.11 weight percent zinc iodide.

The catalyst compositions set forth in the examples of Table I were prepared using the procedures described in the preceding examples. The Weight Percent given in Table I refers to the weight percent of the quaternary onium iodide present based on the total weight of the catalyst. The zinc oxide and silica used as the support materials were the same as the support materials described in Examples 1 and 3.

                  TABLE I                                                          ______________________________________                                                                             Weight                                     Example                                                                               Quaternary Onium Iodide                                                                            Support  Percent                                    ______________________________________                                         4      Tetrapropylammonium iodide                                                                         ZnO      15.8                                       5      Tetrabutylammonium iodide                                                                          ZnO      22                                         6      Tetrapentylammonium iodide                                                                         ZnO      20.4                                       7      Tetrahexylammonium iodide                                                                          ZnO      22.5                                       8      Tetraoctylammonium iodide                                                                          ZnO      26.0                                       9      Tetradecylammonium iodide                                                                          ZnO      18.0                                       10     Tetradodecylammonium iodide                                                                        ZnO      21.0                                       11     Trioctylammonium iodide                                                                            ZnO      21.0                                       12     Dioctylammonium iodide                                                                             ZnO      18.0                                       13     Octylammonium iodide                                                                               ZnO      13.0                                       14     N,N'-Dimethyl-N,N'-hexa-                                                                           ZnO      20.0                                              decylpiperizinium diiodide                                              15     N,N-Dimethyl-N-hexadecyl-N-                                                                        ZnO      19.0                                              [3-pyrrolidinonopropyl]-                                                       ammonium iodide                                                         16     N,N,N,N',N',N'-hexa-(dodecyl)-                                                                     ZnO      30.0                                              octane-1,4-diammonium diiodide                                          17     N,N,N,N',N',N'-hexa-(dodecyl)-                                                                     ZnO      29.0                                              butane-1,4-diammonium diiodide                                          18     N-Octylpyridinium iodide                                                                           ZnO      16.0                                       19     Tetraoctylphosphonium iodide                                                                       SiO.sub.2                                                                               11.0                                       20     Tetrabutylphosphonium iodide                                                                       SiO.sub.2                                                                               11.0                                       21     Tetradodecylammonium iodide                                                                        SiO.sub.2                                                                               11.0                                       ______________________________________                                    

The catalysts set forth in Table II were prepared from a quaternary onium iodide compound, a Lewis acid co-catalyst and a support material according to the procedures described in Examples 1-3. The Weight Percent given for each example refers to the weight of the co-catalyst present on the supported catalyst based on the total weight of the catalyst. The materials described in Examples 1 and 3 were used as the catalyst supports. The onium iodide compound and the weight percent thereof present on each catalyst and the support material of each of the Table II examples were:

                  TABLE II                                                         ______________________________________                                                                   Weight                                               Example      Co-catalyst  Percent                                              ______________________________________                                         22           ZnI.sub.2    0.22                                                 23           ZnCl.sub.2   0.22                                                 24           SnI.sub.2    0.27                                                 25           SnI.sub.2    0.54                                                 26           SnI.sub.2    1.10                                                 27           MgI.sub.2    0.22                                                 28           MnI.sub.2    0.22                                                 29           ZrI.sub.4    0.27                                                 30           TiI.sub.4    0.22                                                 31           Titanium tetra-                                                                             0.22                                                              isopropoxide                                                      32           Iron (III) acetyl-                                                                          0.11                                                              acetonate                                                         33           ZnI.sub.2    1.7                                                  34           SnI.sub.2    2.2                                                  35           SnI.sub.4    1.8                                                  36           LiI          1.5                                                  37           ZnI.sub.2    0.9                                                  38           ZnI.sub.2    3.4                                                  39           ZnI.sub.2    8.5                                                  40           SnI.sub.2    0.27                                                 41           SnI.sub.2    0.54                                                 42           SnI.sub.2    1.1                                                  43           ZnI.sub.2    0.055                                                44           ZnI.sub.2    0.11                                                 45           ZnI.sub.2    0.15                                                 46           ZnI.sub.2    0.23                                                 47           ZnI.sub.2    0.55                                                 48           SnI.sub.2    0.11                                                 49           ZnI.sub.2    0.11                                                 50           ZnI.sub.2    0.55                                                 51           ZnI.sub.2    2.3                                                  ______________________________________                                          Examples 22-32: 11% Tetradodecylammonium iodide on                             Examples 33-42: 26% Tetraoctylammonium iodide on ZnO                           Examples 43-48: 11% Tetraoctylphosphonium iodide on SiO.sub.                   Examples 49-51: 11% Tetrabutylphosphonium iodide on SiO.sub.2            

The supported catalysts described in Example 52-57 were prepared by procedures analogous to Example 3 using the silica support material described in Example 3, zinc iodide and the quaternary ammonium iodide compound given in each example. Each catalyst contained 11 weight percent of the quaternary ammounium iodide compound and 0.11 weight percent zinc iodide, based on the total weight of the catalyst.

EXAMPLE 52

N-Hexyl-1,4-diazabicyclo[2.2.2]octane iodide

EXAMPLE 53

N-Tetradecyl-1,4-diazabicyclo[2.2.2]octane iodide

EXAMPLE 54

N-Hexyl-1,4-diazabicyclo[2.2.2]octane iodide hydroiodide

EXAMPLE 55

N-Octylazabicyclo[2.2.2]octane iodide

EXAMPLE 56

N-Methyl-N-dodecylpyrrolidinium iodide

EXAMPLE 57

Tetrakis-(3-methylbutyl)ammonium iodide

The supported catalysts described in Example 58-71 were prepared by procedures analogous to and using the silica support material described in Example 3, zinc iodide and the quaternary phosphonium iodide compound given in each example. Each catalyst contained 11 weight percent of the quaternary phosphonium iodide compound and 0.11 (Examples 58 and 60) or 0.055 (Examples 59 and 61-72) weight percent zinc iodide, based on the total weight of the catalyst.

EXAMPLE 58

Tribenzyl(octyl)phosphonium iodide

EXAMPLE 59

Triphenyl(hexyl)phosphonium iodide

EXAMPLE 60

Tribenzyl(dodecyl)phosphonium iodide

EXAMPLE 61

Triphenyl(octyl)phosphonium iodide

EXAMPLE 62

Triphenyl(decyl)phosphonium iodide

EXAMPLE 63

Triphenyl(dodecyl)phosphonium iodide

EXAMPLE 64

Tris(2-methylpropyl)(butyl)phosphonium iodide

EXAMPLE 65

Tris(2-methylpropyl)(3-methylbutyl)phosphonium iodide

EXAMPLE 66

Tris(3-chlorophenyl)(dodecyl)phosphonium iodide

EXAMPLE 67

Triphenyl(3-methylbutyl)phosphonium iodide

EXAMPLE 68

Triphenyl(trimethylsilylmethyl)phosphonium iodide

EXAMPLE 69

Tris(2,4,6-trimethylphenyl)(hexyl)phosphonium iodide

EXAMPLE 70

Tris(2,4,6-trimethylphenyl)(dodecyl)phosphonium iodide

EXAMPLE 71

Tris(2,4,6-trimethylphenyl)(tetradecyl)phosphonium iodide

EXAMPLE 72

Tetrakis(2-methylpropyl)phosphonium iodide

EXAMPLE 73

Silica support material described in Example 3 was contacted with tetraoctylphosphonium iodide, tetradodecylammonium iodide and zinc iodide to obtain a supported catalyst bearing 5.5 weight percent tetraoctylphosphonium iodide, 5.5 weight percent tetradodecylammonium iodide and 0.22 weight percent zinc iodide.

Examples 74-83 describe supported catalysts prepared from a quaternary ammonium compound and a variety of support materials. The percent given in each of the examples refers to the weight percent of the quaternary ammonium compound specified on the support based on the total weight of the catalyst. The catalysts of Examples 78-83 also contained 0.23 weight percent zinc iodide.

EXAMPLE 74

26% Tetraoctylammonium iodide on silicon nitride powder having a surface area of 11.9 m² /g and a mean particle size of 60 microns.

EXAMPLE 75

26% Tetraoctylammonium iodide on boron nitride powder having a surface area of 2.9 m² /g, a bulk density of 2.1 g/cm³ and a particle diameter in the range of 50-100 microns.

EXAMPLE 76

22% Tetrabutylammonium iodide on zinc carbonate powder having a particle diameter in the range of 75-150 microns.

EXAMPLE 77

22% Tetrabutylammonium iodide on magnesium oxide powder having a surface area of 1.0 m² /g and a particle diameter in the range of 75-150 microns.

EXAMPLE 78

11% Tetradodecylammonium iodide on alumina (Calsicat SE) spheres: 1/8" diameter spheres with a surface area of 10 m² /g, a total pore volume =0.44 cc (Hg)/g, packing density of 0.81 g/cm³, crush strength =18 lbs, and a general composition by weight percent of: Al₂ O₃ =99.7, SiO₂ =0.1, Na₂ O=0.1 and Fe₂ O₃ =0.08.

EXAMPLE 79

11% Tetradodecylammonium iodide on alumina (Norton 5552) rings 1/4" rings having a surface area of 0.43 m² /g, a total pore volume of 0.37 cc (Hg)/gm, a median pore diameter of 7μ, a packing density of 0.80 g/cm³, and a chemical composition by weight percent of: Al₂ O₃ =93.1, SiO₂ =5.6, Fe₂ O₃ =0.3, TiO₂ =0.1, CaO=0.1, MgO=0.3, Na₂ O=0.1, K₂ O=0.1.

EXAMPLE 80

11% Tetradodecylammonium iodide on alumina (Norton 08228) pellets: 3/16" diameter pellets with a surface area of 0.25 m² /g, a total pore volume of 0.23 cc (Hg)/gm, a median pore diameter of 19μ, a packing density of 0.90 g/cm³, and a chemical composition by weight percent of: Al₂ O₃ =84.7, SiO₂ =13.4, Fe₂ O₃ =0.21, TiO₂ =0.47, CaO=0.21, MgO=0.12, Na₂ O =0.15, K₂ O=0.26.

EXAMPLE 81

11% Tetradodecylammonium iodide on zinc oxide (Calsicat ZnO) extrudate: 1/8" diameter extrudate with a surface area of 3.0 m² /g, a packing density of 1.5 g/cm³, a crush strength of 11 pounds, and a nominal chemical composition of 100% ZnO.

EXAMPLE 82

18% Tetradecylammonium iodide on alumina (Norton 82326) spheres: 3/16" diameter spheres having a surface area of 0.39 m² /g, a total pore volume of 0.36 cc(Hg)/g, a median pore diameter of 5.4 microns, a packing density of 0.94 g/cm³, and a chemical composition by weight percent of: Al₂ O₃ =93.1, SiO₂ =5.6, Fe₂ O₃ =0.3, MgO=0.3, TiO₂ =0.1 and Na₂ O=0.1.

EXAMPLE 83

18% Tetradecylammonium iodide on titanium dioxide (Degussa) extrudate: 1/16" diameter extrudate having a surface area of 50 m² /g and a chemical composition by weight percent of: TiO₂ =99.5, Al₂ O₃ =0.3, and SiO₂ =0.2.

The following examples illustrate the preparation of the catalyst compositions comprising an organic onium iodide and an organotin halide on a catalyst support material.

EXAMPLE 84

Triphenyl(hexyl)phosphonium iodide (0.75 g) and triphenyltin iodide (0.0151 g) were placed in a 50 mL flask and dissolved in 30 mL of anhydrous methanol at 30° C. To this solution was added 6.0 g of silica support. The silica support material was prepared by grinding silica pellets 0.1875 inch in diameter and classifying the ground material and using the portion which passed a 10 mesh sieve and was retained on a 20 mesh. The flask was placed on a rotary evaporator and agitated for 20 minutes with the flask in the bath at 50° C. Methanol was removed while the flask was in the 60° C. bath using vacuum. The supported catalyst obtained (6.75 g) contained 11 weight percent triphenyl(hexyl)phosphonium iodide and 0.22 weight percent triphenyltin iodide.

EXAMPLE 85

A supported catalyst consisting of 11 weight percent tetradodecylammonium iodide and 0.22 weight percent tributyltin iodide on silica was prepared according to the general procedure described in Example 84.

EXAMPLE 86

A supported catalyst consisting of 11 weight percent tetradodecylammonium iodide and 1.1 weight percent triphenyltin iodide on silica was prepared according to the general procedure described in Example 84.

ISOMERIZATION OF EPOXYBUTENES

The supported catalysts described hereinabove were used to isomerize 3,4-epoxy-1-butene under steady state conditions in a 1 atmosphere, single-pass flow reactor system. The reactor tube was constructed of Pyrex glass and the catalyst charge (between 0.1 and 20.0 g) was held in place by means of a Pyrex glass frit. The geometries of the reactor and catalyst particles as well as bed depth were chosen to maintain and measure the true kinetic and catalytic aspects of the reaction. Gas hourly space velocities (GHSV, mL gas fed per hour per mL catalyst) for all experiments fell within the range of about 30 up to 3000. A chromel/alumel thermocouple sheathed in stainless steel was embedded within the catalyst bed to measure the true reaction temperature.

The 3,4-epoxy-1-butene reactant was added by flowing helium through a liquid-vapor saturator containing the liquid reactant. The reactant was maintained at constant temperature by coupling the saturator to a refrigerated constant temperature circulator bath which was capable of maintaining the temperature of the liquid-vapor saturator at ±1° C. accuracy from -10° C. to +120° C. The helium flow used to sweep the 3,4-epoxy-1-butene vapor from the saturator to the reactor inlet was maintained using a mass flow controller over the range 2-100 mL (standard temperature and pressure) per minute. The feed compositions fed to the reactor consisted of from 0.01 to 0.33 bar 3,4-epoxy-1-butene pressure (absolute) with the balance He to give a total pressure of approximately 1 to 1.5 bar at GHSV ranging from 30 to 3000. Reaction product analyses (as well as feed composition analyses) were made using an in-line gas sampling loop connected directly to the inlet of a Varian 3760 gas chromatograph. The reaction products were analyzed using a packed Chromosorb 101 column (8 feet by 2 mm interior diameter Pyrex glass capillary column) connected to a flame ionization detector.

Further, by means of a switching valve, it was possible to divert the feed stream through the in-line sample loop prior to passage over the catalyst. In this way, quantitative analysis of the feed stream and comparison to the corresponding data from the reactor effluent were possible, thereby providing very accurate measurements of both conversion levels and product selectivities. Output from the flame ionization (FI) detector was integrated using a computing integrator which was programmed to give both absolute quantities and rates of formation. All reactor exit lines were heated and maintained at 125°-140° C. to prevent product condensation.

The GC analysis was performed using the following temperature programming schedule: an initial temperature of 100° C. was held for 2 minutes, followed by a temperature program rate of +10° C. per minute up to a final temperature of 200° C. which was held for 7 minutes. The helium GC carrier rate was 20 mL per minute.

The catalyst and conditions employed and the results obtained in each of the isomerization experiments are set forth in Tables III and IV wherein Temp is the temperature in ° C. at which the reaction occurred, Press is the 3,4-epoxy-1-butene partial pressure in bars absolute of the gas fed, GHSV is defined above, Conv is the mole percent of moles 3,4-epoxy-1-butene converted to other compounds per moles of 3,4-epoxy-1-butene fed and Select is the mole percent of 3,4-epoxy-1-butene converted to 2,5-dihydrofuran based on the moles of 3,4-epoxy-1-butene converted.

EXAMPLE 87-114

These examples demonstrate the use of supported catalysts bearing only a quaternary onium iodide as the catalytic component. In Examples 87-96 and Examples 99-101 the catalysts were subjected to a pretreatment at elevated temperatures in an inert atmosphere for 30-60 minutes prior to starting the reactant feed. The pretreatments were performed at 140° C. except in Examples 87 and 88 wherein temperatures of 160° C. and 150° C., respectively, were used.

                  TABLE III                                                        ______________________________________                                                Catalyst                                                                Example                                                                               of Example                                                                               Temp    Press GHSV  Conv  Select                              ______________________________________                                         87     4         130     0.03  240   6     21                                  88     1         140     0.03  240   48    68                                  89     5         140     0.03  240   49    68                                  90     5         160     0.03  240   52    63                                  91     6         140     0.03  240   28    78                                  92     7         140     0.03  240   17    83                                  93     8         130     0.03  240   41    94                                  94     8         125     0.03  540   9     91                                  95     8         130     0.03  540   13    94                                  96     8         140     0.03  540   26    95                                  97     9         130     0.03  240   58    90                                  98     10        130     0.03  240   78    94                                  99     11        130     0.03  240   79    69                                  100    12        130     0.03  300   73    40                                  101    13        130     0.03  300   67    61                                  102    14        130     0.03  300   5     31                                  103    14        170     0.03  300   82    58                                  104    15        130     0.03  300   2     3                                   105    15        167     0.03  300   55    65                                  106    16        130     0.03  300   49    94                                  107    16        130     0.09  300   32    91                                  108    17        130     0.03  300   97    90                                  109    17        130     0.03  600   93    90                                  110    18        130     0.03  240   72    80                                  111    19        120     0.03  300   1     19                                  112    19        130     0.03  300   2     31                                  113    19        140     0.03  300   2     41                                  114    20        160     0.03  300   0.4   54                                  ______________________________________                                    

EXAMPLES 115-250

These examples demonstrate the favorable effect of using a Lewis acid co-catalyst in conjunction with a quaternary onium iodide compound as evidenced by an increase in the conversion of the 3,4-epoxy-1-butene reactant and/or increasing the selectivity to the desired 2,5-dihydrofuran. In Examples 137-140 the catalysts were subjected to a pretreatment in flowing helium at 140° C. for 30-60 minutes prior to starting the reactant feed.

                  TABLE IV                                                         ______________________________________                                                Catalyst                                                                Example                                                                               of Example                                                                               Temp    Press GHSV  Conv  Select                              ______________________________________                                         115    2         125     0.17  75    64    91                                  116    2         125     0.17  190   38    94                                  117    2         130     0.17  75    83    93                                  118    2         130     0.17  190   50    93                                  119    2         130     0.17  750   14    92                                  120    21        120     0.09  300   0.2   36                                  121    21        130     0.09  300   0.3   45                                  122    21        140     0.09  300   0.6   67                                  123    22        130     0.09  300   28    93                                  124    23        130     0.09  300   15    87                                  125    24        120     0.09  300   5     99                                  126    24        130     0.09  300   7     99                                  127    24        140     0.09  300   8     98                                  128    25        120     0.09  300   7     94                                  129    25        130     0.09  300   12    93                                  130    26        120     0.09  300   10    96                                  131    27        130     0.09  300   6     75                                  132    28        130     0.09  300   8     93                                  133    29        130     0.09  300   15    98                                  134    30        130     0.09  300   2     95                                  135    31        130     0.09  300   6     71                                  136    32        130     0.09  300   8     95                                  137    33        130     0.03  300   86    90                                  138    34        130     0.03  300   84    85                                  139    35        130     0.03  300   56    72                                  140    36        130     0.03  300   73    85                                  141    37        130     0.03  300   62    89                                  142    38        130     0.03  300   90    82                                  143    39        130     0.03  300   92    62                                  144    40        120     0.09  300   7     99                                  145    40        140     0.09  300   8     98                                  146    41        120     0.09  300   13    94                                  147    42        120     0.09  300   10    96                                  148    42        130     0.09  300   15    65                                  149    43        130     0.09  300   12    97                                  150    44        130     0.09  300   16    95                                  151    44        130     0.13  300   15    95                                  152    45        120     0.09  60    79    98                                  153    45        120     0.09  240   35    95                                  154    46        120     0.09  300   30    97                                  155    46        130     0.09  300   32    96                                  156    46        140     0.09  300   37    94                                  157    47        120     0.09  300   55    85                                  158    48        120     0.09  300   7     93                                  159    48        130     0.09  300   11    94                                  160    49        120     0.09  300   18    97                                  161    49        130     0.09  300   23    96                                  162    50        120     0.09  300   54    85                                  163    51        125     0.03  300   92    80                                  164    51        135     0.03  300   93    75                                  165    51        150     0.03  300   96    68                                  166    52        140     0.09  300   10    85                                  167    52        150     0.09  300   16    85                                  168    52        160     0.09  300   23    83                                  169    53        140     0.09  300   6     91                                  170    53        150     0.09  300   12    88                                  171    53        160     0.09  300   26    86                                  172    53        170     0.09  300   44    80                                  173    53        180     0.09  300   56    75                                  174    54        131     0.09  300   18    80                                  175    54        141     0.09  300   27    82                                  176    55        130     0.09  300   9     88                                  177    55        140     0.09  300   11    90                                  178    55        160     0.09  300   13    82                                  179    56        120     0.09  300   10    75                                  180    57        120     0.09  300   10    88                                  181    57        130     0.09  300   13    87                                  182    57        140     0.09  300   18    87                                  183    57        160     0.09  300   34    88                                  184    3         130     0.09  300   17    85                                  185    3         140     0.09  300   27    86                                  186    3         150     0.09  300   42    88                                  187    3         160     0.09  300   50    86                                  188    3         170     0.09  300   57    85                                  189    58        120     0.09  300   18    93                                  190    58        130     0.09  300   26    94                                  191    58        140     0.09  300   30    94                                  192    58        150     0.09  300   43    93                                  193    59        130     0.09  60    38    89                                  194    59        140     0.09  60    84    89                                  195    59        140     0.09  120   60    91                                  196    60        130     0.09  300   35    95                                  197    60        160     0.09  300   55    92                                  198    61        140     0.09  300   26    90                                  199    61        160     0.09  300   41    90                                  200    62        140     0.09  300   30    92                                  201    62        160     0.09  300   45    90                                  202    63        130     0.09  300   37    94                                  203    64        130     0.09  300   27    90                                  204    65        140     0.09  300   24    92                                  205    66        140     0.09  300   26    79                                  206    67        130     0.09  300   9     61                                  207    67        170     0.09  300   15    75                                  208    68        140     0.09  300   11    62                                  209    69        160     0.09  300   12    71                                  210    69        180     0.09  300   68    95                                  211    70        160     0.09  300   64    93                                  212    71        140     0.09  300   34    95                                  213    71        160     0.09  300   50    94                                  214    72        140     0.09  300   12    80                                  215    72        160     0.09  300   28    85                                  216    73        125     0.09  300   21    95                                  217    73        130     0.09  300   37    94                                  218    74        130     0.03  540   5     81                                  219    74        150     0.03  540   20    80                                  220    75        130     0.09  540   3     80                                  221    75        130     0.03  540   7     80                                  222    75        160     0.03  540   29    73                                  223    76        140     0.03  240   15    50                                  224    76        160     0.03  240   50    49                                  225    77        140     0.03  540   10    35                                  226    77        160     0.03  540   15    41                                  227    77        170     0.03  240   59    61                                  228    78        125     0.17  150   65    51                                  229    79        125     0.09  75    55    86                                  230    79        125     0.09  190   29    84                                  231    80        125     0.17  90    68    93                                  232    80        125     0.17  250   34    92                                  233    80        125     0.17  500   16    93                                  234    80        125     0.17  1000  8     93                                  235    80        130     0.17  1000  18    93                                  236    81        125     0.17  250   8     78                                  237    81        130     0.17  250   13    85                                  238    82        130     0.03  60    11    64                                  239    82        135     0.03  60    25    77                                  240    82        140     0.03  60    48    83                                  241    83        130     0.03  160   32    63                                  242    83        135     0.03  160   36    64                                  243    83        140     0.03  160   53    67                                  244    84        150     0.09  600   8     81                                  245    84        160     0.09  600   10    78                                  246    85        130     0.09  300   14    98                                  247    85        130     0.09  600   8     98                                  248    85        140     0.09  300   22    98                                  249    86        130     0.09  300   13    99                                  250    86        140     0.09  300   26    98                                  ______________________________________                                    

EXAMPLE 251-255

Using the catalyst of Example 2 and the isomerization procedure described hereinabove, two other γ,δ-epoxyalkenes and a γ,δ-epoxycycloalkene were isomerized to 2,5-dihydrofuran compounds. The reactants used and the desired dihydrofuran product obtained were:

    ______________________________________                                         Example  Reactant       Dihydrofuran Product                                   ______________________________________                                         251,252  2-Methyl-3,4-epoxy-                                                                           3-methyl-2,5-dihydro-                                           1-butene       furan                                                  253,254  2,3-Dimethyl-3,4-                                                                             3,4-Dimethyl-2,5-di-                                            epoxy-1-butene dihydrofuran                                           255      3,4-epoxycyclo-                                                                               9-oxa-bicyclo[4.2.1]-                                           octene         non-7-ene                                              ______________________________________                                    

The results obtained are set forth in Table V wherein Conv is the mole percent of moles of reactant converted to other products per moles of reactant fed and Select is the percent moles of reactant converted to the desired 2,5-dihydrofuran product based on the moles of reactant converted.

                  TABLE V                                                          ______________________________________                                         Example Temp     Press    GHSV   Conv   Select                                 ______________________________________                                         251     126      0.04     60     65     66                                     252     126      0.04     120    46     67                                     253     127      0.03     60     51     81                                     254     127      0.05     60     46     81                                     255     130      0.01     60     61     90                                     ______________________________________                                    

EXAMPLE 256-300

These examples demonstrate the use of the unsupported catalyst systems of this invention in the isomerization of 3,4-epoxy-1-butene to 2,5-dihydrofuran according to the general procedure described relative to the preceding isomerization examples. Because the catalyst can exist in a substantially molten state if the process is operated above the melting point of the quaternary onium iodide salt, the reactor was operated in an upward flow mode whereby the gaseous feed entered below the catalyst bed and passed through a gas dispersion frit upon which the unsupported catalyst system was supported to maintain the catalyst in the proper position in the reactor. Alternatively, the catalyst was maintained in a vessel with a closed bottom into which the feed gas was added below the level of the substantially molten catalyst by means of a gas dispersion apparatus. In both reactor configurations, the gaseous reactor effluent comprising unreacted feed and product exited the top of the reactor into the downstream assembly described hereinabove.

In the examples utilizing an unsupported catalyst system, the catalyst components were heated in an inert gas flow, typically 100 mL (STP) per minute of helium, until both catalyst components existed in a molten state. At this point, a partial pressure of 3,4-epoxy-1-butene was introduced into the carrier gas stream and the catalytic reaction as initiated. Typical molar concentrations of 3,4-epoxy-1-butene in the carrier gas varied from 3 to 25%, with 9 to 10% being the most commonly used feed concentration.

The unsupported catalyst systems listed below were prepared by physically and intimately mixing the components while in the solid state and were used in Examples 256-326. For catalyst components which were potentially air sensitive, care was taken to prevent contact with air while loading into the catalytic reactor.

    ______________________________________                                         (i)    Tetradodecylammonium iodide (1.20 g) and zinc                                  iodide (24.0 mg)                                                        (ii)   Triphenyl(hexyl)phosphonium iodide (1.00 g) and                                zinc iodide (5.0 mg)                                                    (iii)  Triphenyl(hexyl)phosphonium iodide (0.50 g),                                   tris-(2,4,6-trimethylphenyl)(hexyl)phosphonium                                 iodide (0.50 g) and zinc iodide (5.0 mg)                                (iv)   Tetradodecylammonium iodide (20.0 g) and                                       tributyltin iodide (0.52 g)                                             (v)    Tetradodecylammonium iodide (10.0 g) and                                       dibutyltin diiodide (0.30 g)                                            (vi)   Tetradodecylammonium iodide (10.0 g) and                                       triphenyltin iodide (0.29 g)                                            (vii)  Triphenyl(hexyl)phosphonium iodide (10.0 g) and                                tributyltin iodide (0.07 g)                                             (viii) Triphenyl(hexyl)phosphonium iodide (10.0 g) and                                dibutyltin diiodide (0.21 g)                                            (ix)   Tetradodecylammonium iodide (10.0 g) and                                       trioctyltin iodide (0.36 g)                                             (x)    Triphenyl(hexyl)phosphonium iodide (10.0 g) and                                trioctyltin iodide (0.25 g)                                             (xi)   Tetrabutylarsonium iodide (8.00 g) and                                         trioctyltin iodide (0.54 g)                                             (xii)  Tetraoctylarsonium iodide (8.00 g) and                                         trioctyltin iodide (0.38 g)                                             (xiii) Triphenyl(hexyl)phosphonium iodide (11.6 g) and                                triphenyltin iodide (0.24 g)                                            (xiv)  Triphenyl(hexyl)phosphonium iodide (11.6 g) and                                triphenyltin iodide (0.59 g)                                            (xv)   Triphenyl(hexyl)phosphonium iodide (11.6 g) and                                triphenyltin iodide (2.33 g)                                            (xvi)  Triphenyl(hexyl)phosphonium iodide (6.0 g) and                                 triphenyltin iodide (6.0 g)                                             (xvii) Triphenyl(hexyl)phosphonium iodide (2.0 g) and                                 triphenyltin iodide (10.0 g)                                            (xviii)                                                                               Triphenyl(hexyl)phosphonium iodide (0.60 g) and                                triphenyltin iodide (11.4 g)                                            (xix)  Triphenyl(hexyl)phosphonium iodide (0.10 g) and                                triphenyltin iodide (10.0 g)                                            (xx)   Triphenyl(hexyl)phosphonium iodide (2.0 g) and                                 tricyclohexyltin iodide (10.4 g)                                        (xxi)  Triphenyl(hexyl)phosphonium iodide (2.0 g) and                                 tribenzyltin iodide (10.9 g)                                            ______________________________________                                    

The ratio of zinc oxide to quaternary onium iodide compound(s) in each of catalyst systems (i) and (ii) is the same as the analogous ratio for the supported catalysts of Examples 22 and 59, respectively.

                  TABLE VI                                                         ______________________________________                                                Catalyst                                                                Example                                                                               System   Temp    Press GHSV   Conv  Select                              ______________________________________                                         256    (i)      110     0.09  500    17    77                                  257    (i)      120     0.09  500    44    90                                  258    (i)      130     0.09  500    60    93                                  259    (i)      140     0.09  500    88    94                                  260    (ii)     140     0.09  1200   25    91                                  261    (ii)     150     0.09  1200   30    90                                  262    (ii)     160     0.09  1200   36    87                                  263    (ii)     160     0.09  2400   18    91                                  264    (iii)    130     0.09  600    17    82                                  265    (iii)    140     0.09  600    43    92                                  266    (iii)    160     0.09  600    59    86                                  267    (iii)    180     0.09  600    72    80                                  268    (iv)     130     0.09  120    95    95                                  269    (iv)     130     0.09  300    75    98                                  270    (iv)     130     0.09  600    60    99                                  271    (v)      130     0.09  240    96    96                                  272    (v)      130     0.09  600    83    97                                  273    (v)      130     0.09  1200   34    96                                  274    (vi)     130     0.09  240    98    98                                  275    (vi)     130     0.09  600    78    99                                  276    (vi)     130     0.09  1200   55    99                                  277    (vi)     140     0.09  240    98    95                                  278    (vi)     140     0.09  600    89    98                                  279    (vi)     140     0.09  1200   75    98                                  280    (vii)    140     0.09  120    68    81                                  281    (vii)    140     0.09  600    24    88                                  282    (viii)   130     0.09  240    71    93                                  283    (viii)   130     0.09  600    37    94                                  284    (viii)   130     0.09  1200   21    94                                  285    (viii)   140     0.09  240    80    90                                  286    (viii)   140     0.09  1200   22    92                                  287    (ix)     130     0.09  600    40    99                                  288    (ix)     130     0.09  1200   20    98                                  289    (ix)     140     0.09  600    68    98                                  290    (ix)     140     0.09  1200   46    99                                  291    (ix)     140     0.09  240    89    96                                  292    (x)      130     0.09  300    53    90                                  293    (x)      130     0.09  600    30    92                                  294    (x)      130     0.09  1200   14    94                                  295    (x)      140     0.09  600    43    91                                  296    (x)      140     0.09  1200   20    93                                  297    (xi)     130     0.09  300    80    97                                  298    (xi)     130     0.09  600    65    98                                  299    (xii)    130     0.09  300    28    98                                  300    (xii)    130     0.09  600    18    98                                  301    (xiii)   130     0.10  300    38    93                                  302    (xiii)   130     0.10  600    22    94                                  303    (xiv)    130     0.10  300    80    93                                  304    (xiv)    130     0.10  600    67    93                                  305    (xiv)    140     0.10  300    88    92                                  306    (xiv)    140     0.10  600    74    92                                  307    (xv)     130     0.10  300    87    95                                  308    (xv)     130     0.10  600    69    95                                  309    (xv)     140     0.10  300    91    95                                  310    (xv)     140     0.10  600    71    94                                  311    (xv)     140     0.25  600    64    95                                  312    (xvi)    130     0.10  300    100   97                                  313    (xvi)    130     0.10  600    99    97                                  314    (xvii)   130     0.10  300    100   98                                  315    (xvii)   130     0.10  600    100   98                                  316    (xvii)   130     0.25  300    99    97                                  317    (xvii)   130     0.25  1000   91    97                                  318    (xviii)  130     0.10  300    80    97                                  319    (xviii)  130     0.10  600    67    97                                  320    (xviii)  130     0.25  600    62    97                                  321    (xix)    130     0.10  300    68    96                                  322    (xix)    130     0.10  600    56    96                                  323    (xx)     130     0.10  300    14    96                                  324    (xx)     130     0.10  600    9     96                                  325    (xxi)    130     0.10  300    70    85                                  326    (xxi)    130     0.10  600    54    81                                  ______________________________________                                    

EXAMPLES 327-331

The following examples illustrate the isomerization of 3,4-epoxy-1-butene to 2,5-dihydrofuran using the catalyst solutions described hereinabove. The gas chromatographic (GC) analyses were performed on a Hewlett-Packard 5890A gas chromatograph with a DB5-30W capillary column; temperature program 35° C. (4.5 minutes), 20° C./minute to 260° C. (hold 6 minutes). 1H NMR analyses were performed on a Varian Gemini 300 spectrometer (300 MHz) using CDCl3 as solvent and tetramethylsilane as internal standard.

EXAMPLE 327

To a nitrogen-purged, 500-mL, four-neck flask equipped with a thermometer, addition funnel, condenser, magnetic stirrer, and heating mantle was charged 170.57 g of p-xylene, 21.62 g (0.05185 moles) of tributyltin iodide, and 39.76 g (0.07394 moles) of tetraheptylammonium iodide. The mixture was heated to 109° C. and 34.04 g (0.4857 moles) of 3,4-epoxy-1-butene was added dropwise over 15 minutes at 109°-117° C. Thirty minutes after the addition the reaction was complete as shown by GC. After cooling, the condenser was replaced with a fractional distillation apparatus and the mixture distilled. A 36.81 g fraction boiling at 62°-134° C. was collected which had the following GC assay: 0.11% furan, 0.32% 3,4-epoxy-1-butene, 1.32% crotonaldehyde, 88.86% 2.5-dihydrofuran, and 9.39% p-xylene. The yield of 2,5-dihydrofuran was 96.1%.

EXAMPLE 328

To a nitrogen-purged, 500-mL, four-neck flask equipped with a thermometer, addition funnel, condenser, magnetic stirrer, and heating mantle was charged 213.58 g of p-xylene, 28.81 g (0.06910 moles) of tributyltin iodide, and 32.27 g (0.05785 moles) of dodecyltriphenylphosphonium iodide. The mixture was heated to 110° C. and 34.66 g (0.4945 moles) of 3,4-epoxy-1-butene was added dropwise over 18 minutes at 110°-119° C. Thirty-five minutes after the addition the reaction was complete as shown by GC. After cooling, the condenser was replaced with a fractional distillation apparatus and the mixture distilled. A 35.22 g fraction boiling at 59°-105° C. was collected which had the following GC assay: 0.2% 3,4-epoxy-1.butene, 0.4% crotonaldehyde, 87.2% 2.5-dihydrofuran, and 8.6% p-xylene. The yield of 2,5-dihydrofuran was 87.2%.

EXAMPLE 329

The process of this invention may be operated continuously as shown by this example. The continuous reaction system consists of a heated, plug-flow reactor (465 mL, U-tube of Pyrex glass) into which the 3,4-epoxy-1-butene and recirculated catalyst solution is pumped. After a residence time in the reactor at the rearrangement temperature the homogeneous reaction stream feeds into the center of a fractional distillation column. The volatile materials are condensed with a water-cooled condenser and collected in the receiver. The stripped catalyst solution from the distillation pot is returned to the reactor along with fresh 3,4-epoxy-1-butene. This system was charged with a solution of 41.7 g (0.100 mole) of tributyltin iodide, 47.4 g (0.123 mole) of tetrabutylphosphonium iodide, and 525 mL of o-dichlorobenzene. The reactor tube was heated to 130° C. and the distillation pot was heated to reflux (pot temperature 205°-213° C.). The catalyst solution was recycled at a rate of 30.2 mL/minute and 3,4-epoxy-1-butene was fed at a rate of 1.2 g/minute giving a total flow rate through the reactor of 32 mL/minute for a reactor residence time of 15 minutes. A total of 400.2 g (5.710 mole) of 3,4-epoxy-1.butene was fed to the system and 371.5 g of distillate (bp 66° C.) was obtained. The distillate had a GC analysis of 92.7% 2,5-dihydrofuran, 2.95% of 3,4-epoxy-1-butene, and 0.48% of crotonaldehyde. The assay yield of 2,5dihydrofuran was 86.1%.

EXAMPLE 330

To a nitrogen-purged, 100-mL, three-neck flask equipped with a thermometer, condenser, magnetic stirrer, and heating mantle was charged 50 mL of p-xylene, 4.35 g (0.0104 moles) of tributyltin iodide, 6.49 g (0.0121 moles) of tetraheptylammonium iodide and 10.28 g (0.1222 moles) of 3,4-epoxy-3-methyl-1-butene. The mixture was heated to reflux (119° C.). After two hours the reaction was complete as judged by GC. After cooling, the condenser was replaced with a distillation head and the mixture distilled. A 17.26 g fraction boiling at 82°-120° C. was collected which had the following NMR weight-percent assay: 70.3% p-xylene, 24.3% 3-methyl-2,5.dihydrofuran, and 5.5% 2-methyl-2butenal. The yield of 3-methyl-2,5-dihydrofuran was 40.8% and the yield of 2-methyl-2-butenal was 9.2%.

EXAMPLE 331

To a nitrogen-purged, 25-mL, three-neck flask equipped with a thermometer, condenser, magnetic stirrer, and heating mantle was charged 12.5 mL of p-xylene, 0.94 g (0.023 moles) of tributyltin iodide, 1.69 g (0.00314 moles) of tetraheptylammonium iodide and 3.10 g (0.0235 moles) of 3,4-epoxycyclooctene (94.1%). The mixture was heated to reflux (125° C.). After five hours the reaction was complete as shown by GC. After cooling, the tetraheptylammonium iodide solids were filtered then the filtrate was filtered through a small pad of silica gel and rinsed with p-xylene. The solvent was distilled off at atmospheric pressure leaving 2.43 g of an oil which had the following NMR weight-percent assay: 42.8% 9-oxabicyclo[4.2.1]non-7-ene and 57.2% p-xylene. The yield of 9-oxabicyclo[4.2.1]non-7-ene was 35.7%.

The invention has been described in detail with particular reference to preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention. 

We claim:
 1. Process for the isomerization of a γ,δ-epoxyalkene or a γ,δ-epoxycycloalkene to the corresponding 2,5-dihydrofuran which comprises contacting a γ,δ-epoxyalkene or a γ,δ-epoxycycloalkene in the gas phase with a catalytic amount of a quaternary organic onium compound containing at least 6 carbon atoms.
 2. Process according to claim 1 wherein the quaternary organic onium compound has the formula ##STR7## wherein each R² independently is selected from hydrogen, alkyl or substituted alkyl moieties having up to about carbon atoms, cycloalkyl or substituted cycloalkyl having about 5 to 20 carbon atoms or aryl or substituted aryl having about 6 to 20 carbon atoms; ferrocenyl; or when Y is P, each R² also may be selected from alkoxy of up to about 20 carbon atoms, cycloalkoxy of about 5 to carbon atoms, aryloxy of 6 to 10 carbon atoms or halogen;two or three R² substituents collectively may represent joined hydrocarbylene groups which form a mono- or poly-cyclic ring with the Y atom to which they are bonded; each R³ is independently selected from hydrocarbylene moieties or substituted hydrocarbylene moieties; x is 0 or 1, and Y is N, P or As; provided that the quaternary onium iodide contains at least 6 carbon atoms.
 3. Process according to claim 2 wherein the process is carried out at a temperature of about 60° to 225° C. and a pressure of about 1.02 to 70 bar.
 4. Process for the isomerization of a γ,δ-epoxyalkene or a γ,δ-epoxycycloalkene having the formula ##STR8## to the corresponding 2,5-dihydrofuran having the formula ##STR9## wherein each R¹ is hydrogen or up to 2 R¹ substituents each may be alkyl of up to about 8 carbon or collectively straight or branched chain alkylene of up to about 8 carbon atoms, which comprises contacting the γ,δ-epoxyalkene or a γ,δ-epoxycycloalkene in the gas phase at a temperature of about 60° to 225° C. and a pressure of about 1.02 to 70 bar with a catalytic amount of a supported quaternary organic onium iodide compound containing at least 6 carbon atoms and having a melting temperature not exceeding about 225° C. and the formula ##STR10## wherein each R² is independently selected from hydrogen, alkyl or substituted alkyl moieties having up to about carbon atoms, cycloalkyl or substituted cycloalkyl having about 5 to 20 carbon atoms, aryl or substituted aryl having about 6 to 20 carbon atoms; ferrocenyl; or when Y is P, each R² also may be selected from alkoxy of up to about 20 carbon atoms, cycloalkoxy of about 5 to carbon atoms, aryloxy of 6 to 10 carbon atoms or halogen;two or three R² substituents collectively may represent joined hydrocarbylene groups which form a mono- or poly-cyclic ring with the Y atom to which they are bonded; each R³ is independently selected from hydrocarbylene moieties or substituted hydrocarbylene moieties; x is 0 or 1, and Y is N, P or As.
 5. Process for the isomerization of a γ,δ-epoxyalkene or a γ,δ-epoxycycloalkene to the corresponding 2,5-dihydrofuran which comprises contacting a γ,δ-epoxyalkene or a γ,δ-epoxycycloalkene in the gas phase with a catalytic amount of a supported catalyst comprising (1) about 0.1 to 30 weight percent of at least one quaternary organic onium iodide compound having at least 6 carbon atoms calculated as weight iodide and based on the total weight of the catalyst and (2) about 0.01 to 30 weight percent, based on the total weight of the catalyst, of a Lewis acid and (3) an essentially nonacidic catalyst support material.
 6. Process for the isomerization of a γ,δ-epoxyalkene or a γ,δ-epoxycycloalkene having the formula ##STR11## to the corresponding 2,5-dihydrofuran having the formula ##STR12## wherein each R¹ is hydrogen or up to 2 R¹ substituents each may be alkyl of up to about 8 carbon or collectively straight or branched chain alkylene of up to about 8 carbon atoms, which comprises contacting the γ,δ-epoxyalkene or a γ,δ-epoxycycloalkene in the gas phase at a temperature of about 60° to 225° C. and a pressure of about 1.02 to 70 bar with a catalytic amount of a supported catalyst comprising (1) at least one quaternary organic onium iodide compound containing at least 6 carbon atoms and having a melting temperature not exceeding about 225° C. and the formula ##STR13## wherein each R² is independently selected from hydrogen, alkyl or substituted alkyl moieties having up to about carbon atoms, cycloalkyl or substituted cycloalkyl having about 5 to 20 carbon atoms, aryl or substituted aryl having about 6 to 20 carbon atoms; ferrocenyl; or when Y is P, each R² also may be selected from alkoxy of up to about 20 carbon atoms, cycloalkoxy of about 5 to carbon atoms, aryloxy of 6 to 10 carbon atoms or halogen;two or three R² substituents collectively may represent joined hydrocarbylene groups which form a mono- or poly-cyclic ring with the Y atom to which they are bonded; each R³ is independently selected from hydrocarbylene moieties or substituted hydrocarbylene moieties; x is 0 or 1, and Y is N, P or As;wherein the quaternary iodide compound, calculated as weight iodide, constitutes 0.1 to 30 weight percent of the total weight of the catalyst; (2) about 0.01 to 10 weight percent, based on the total weight of the catalyst, of an inorganic Lewis acid and (3) an essentially non-acidic catalyst support material.
 7. Process according to claim 6 wherein the catalyst comprises (1) about 0.5 to 20 weight percent, calculated as weight iodide and based on the total weight of the catalyst of at least one quaternary ammonium or phosphonium iodide, (2) about 0.02 to 5.0 weight percent, based on the total weight of the catalyst, of titanium (IV) iodide, zirconium (IV) iodide, zinc iodide or tin (II) iodide and (3) an essentially non-acidic catalyst support material.
 8. Process for the isomerization of a γ,δ-epoxyalkene or a γ,δ-epoxycycloalkene having the formula ##STR14## to the corresponding 2,5-dihydrofuran having the formula ##STR15## wherein each R¹ is hydrogen or up to 2 R¹ substituents each may be alkyl of up to about 8 carbon or collectively straight or branched chain alkylene of up to about 8 carbon atoms, which comprises contacting the γ,δ-epoxyalkene or a γ,δ-epoxycycloalkene in the gas phase at a temperature of about 60° to 225° C. and a pressure of about 1.02 to 70 bar with a catalytic amount of a catalyst comprising a melt of (1) at least one quaternary organic onium iodide compound containing at least 6 carbon atoms and having a melting temperature not exceeding about 225° C. and the formula ##STR16## wherein each R² is independently selected from hydrogen, alkyl or substituted alkyl moieties having up to about 20 carbon atoms, cycloalkyl or substituted cycloalkyl having about 5 to 20 carbon atoms, aryl or substituted aryl having about 6 to 20 carbon atoms; ferrocenyl; or when Y is P, each R² also may be selected from alkoxy of up to about 20 carbon atoms, cycloalkoxy of about 5 to 20 carbon atoms, aryloxy of 6 to 10 carbon atoms or halogen;two or three R² substituents collectively may represent joined hydrocarbylene groups which form a mono- or poly-cyclic ring with the Y atom to which they are bonded; each R³ is independently selected from hydrocarbylene moieties or substituted hydrocarbylene moieties; x is 0 or 1, and Y is N or P; and(2) titanium (IV) iodide, zirconium (IV) iodide, zinc iodide or tin (II) iodide; wherein the weight ratio of (1):(2) is about 200:1 to 5:1.
 9. Process for the isomerization of 3,4-epoxy-1-butene to 2,5-dihydrofuran which comprises contacting the 3,4-epoxy-1-butene in the gas phase at a temperature of about 100° to 200° C. and a pressure of about 1.1 to 20 bar with a catalytic amount of a catalyst comprising one or more quaternary ammonium iodides having the formula ##STR17## wherein each R⁵ substituent independently is selected 15 from alkyl of up to 20 carbon atoms, two R⁵ substituents collectively may represent alkylene of 4 to 6 carbon atoms or alkylene of 4 to 6 carbon atoms substituted with lower alkyl and the quaternary ammonium iodide contains about 16 to 60 carbon atoms.
 10. Process according to claim 9 wherein the catalyst is a supported catalyst comprising (1) about 0.5 to 20 weight percent, calculated as weight iodide and based on the total weight of the catalyst, of one or more quaternary ammonium iodides having the formula ##STR18## wherein each R⁵ substituent is independently selected from alkyl of up to 20 carbon atoms and the quaternary ammonium iodide contains about 16 to 60 carbon atoms, (2) about 0.02 to 5.0 weight percent, based on the total weight of the catalyst of zinc iodide or tin (II) iodide and (3) an essentially non-acidic catalyst support.
 11. A process according to claim 10 wherein the catalyst support material is zinc oxide, silica or alumina.
 12. Process according to claim 9 wherein the catalyst comprises a melt of (1) one or more quaternary ammonium iodides having the formula ##STR19## wherein each R⁵ substituent is independently selected from alkyl of up to 20 carbon atoms and the quaternary ammonium iodide contains about 16 to 60 carbon atoms and (2) zinc iodide or tin (II) iodide; wherein the weight ratio of (1):(2) is about 200:1 to 5:1.
 13. Process for the isomerization of 3,4-epoxy-1-butene to 2,5-dihydrofuran which comprises contacting the 3,4-epoxy-1-butene in the gas phase at a temperature of about 100° to 200° C. and a pressure of about 1.1 to 20 bar with a catalytic amount of a catalyst comprising one or more quaternary ammonium iodides having the formula ##STR20## wherein R⁵ is alkyl of up to about 20 carbon atoms and A is the residue of an azabicycloalkane or diazabicycloalkane having 6 to 12 ring carbon atoms.
 14. Process according to claim 13 wherein the catalyst is a supported catalyst comprising (1) about 0.5 to 20 weight percent, calculated as weight iodide and based on the total weight of the catalyst, of one or more quaternary ammonium iodides having the formula ##STR21## wherein R⁵ is alkyl of up to about 20 carbon atoms and A is the residue of an azabicycloalkane or diazabicycloalkane having 6 to 12 ring carbon atoms, (2) about 0.02 to 5.0 weight percent, based on the total weight of the catalyst of zinc iodide or tin (II) iodide and (3) an essentially non-acidic catalyst support.
 15. A process according to claim 14 wherein the catalyst support material is zinc oxide, silica or alumina.
 16. Process according to claim 13 wherein the catalyst comprises a melt of (1) of one or more quaternary ammonium iodides having the formula ##STR22## wherein R⁵ is alkyl of up to about 20 carbon atoms and A is the residue of an azabicycloalkane or diazabicycloalkane having 6 to 12 ring carbon atoms and (2) zinc iodide or tin (II) iodide; wherein the weight ratio of (1):(2) is about 200:1 to 5:1.
 17. Process for the isomerization of 3,4-epoxy-1-butene to 2,5-dihydrofuran which comprises contacting the 3,4-epoxy-1-butene in the gas phase at a temperature of about 100° to 200° C. and a pressure of about 1.1 to 20 bar with a catalytic amount of a catalyst comprising one or more quaternary phosphonium iodides having the formula ##STR23## wherein each R⁶ substituent is independently selected from alkyl of up to 20 carbon atoms benzyl, phenyl or phenyl substituted with up to 3 substituents selected from lower alkyl, lower alkoxy and halogen and the phosphonium iodide contains about 16 to 60 carbon atoms.
 18. Process according to claim 17 wherein the catalyst is a supported catalyst comprising (1) about 0.5 to 20 weight percent, calculated as weight iodide and based on the total weight of the catalyst, of one or more quaternary phosphonium iodides having the formula ##STR24## wherein each R⁶ substituent is independently selected from alkyl of up to 20 carbon atoms, benzyl, phenyl or phenyl substituted with up to 3 substituents selected from lower alkyl, lower alkoxy and halogen and the phosphonium iodide contains about 16 to 60 carbon atoms, (2) about 0.02 to 5.0 weight percent, based on the total weight of the catalyst of zinc iodide or tin (II) iodide and (3) an essentially non-acidic catalyst support.
 19. A process according to claim 18 wherein the catalyst support material is zinc oxide, silica or alumina.
 20. Process according to claim 17 wherein the catalyst comprises a melt of (1) one or more quaternary phosphonium iodides having the formula ##STR25## wherein and each R⁶ substituent is independently selected from alkyl of up to 20 carbon atoms, benzyl, phenyl or phenyl substituted with up to 3 substituents selected from lower alkyl, lower alkoxy and halogen and the phosphonium iodide contains about 16 to 60 carbon atoms and (2) zinc iodide or tin (II) iodide; wherein the weight ratio of (1):(2) is about 200:1 to 5:1.
 21. Process for the isomerization of a γ,δ-epoxyalkene or a γ,δ-epoxycycloalkene to the corresponding 2,5-dihydrofuran which comprises contacting a γ,δ-epoxyalkene or a γ,δ-epoxycycloalkene in the gas phase with a catalytic amount of a catalyst comprising (1) at least one quaternary organic onium iodide compound having at least 6 carbon atoms and (2) an organotin (IV) compound or organostibonium compound.
 22. Process according to claim 21 for the isomerization of a γ,δ-epoxyalkene or a γ,δ-epoxycycloalkene having the formula ##STR26## to the corresponding 2,5-dihydrofuran having the formula ##STR27## wherein each R¹ is hydrogen or up to 2 R¹ substituents each may be alkyl of up to about 8 carbon or collectively straight or branched chain alkylene of up to about carbon atoms, which comprises contacting the γ,δ-epoxyalkene or a γ,δ-epoxycycloalkene in the gas phase at a temperature of about 60° to 225° C. and a pressure of about 1.02 to 70 bar with a catalytic amount of a catalyst comprising (1) at least one quaternary organic onium iodide compound containing at least 6 carbon atoms and having a melting temperature not exceeding about 225° C. and the formula ##STR28## wherein each R² is independently selected from hydrogen, alkyl or substituted alkyl moieties having up to about 20 carbon atoms, cycloalkyl or substituted cycloalkyl having about 5 to 20 carbon atoms, aryl or substituted aryl having about 6 to 20 carbon atoms; ferrocenyl; or when Y is P, each R² also may be selected from alkoxy of up to about 20 carbon atoms, cycloalkoxy of about 5 to 20 carbon atoms, aryloxy of 6 to 10 carbon atoms or halogen;two or three R² substituents collectively may represent joined hydrocarbylene groups which form a mono- or poly-cyclic ring with the Y atom to which they are bonded; each R³ is independently selected from hydrocarbylene moieties or substituted hydrocarbylene moieties; x is 0 or 1, and Y is N, P or As; (2) at least one organometallic compound having the formula

    (R.sup.7).sub.n --Sn--Hal.sub.(4-n) and (R.sup.7).sub.4 --Sb--Hal

wherein each R⁷ independently is selected from alkyl or substituted alkyl moieties having up to about 20 carbon atoms, cycloalkyl or substituted cycloalkyl having about 5 to 20 carbon atoms, aryl or substituted aryl having about 6 to 20 carbon atoms; Hal is bromo or iodo; and n is 1, 2, 3 or
 4. 23. Process according to claim 22 wherein the catalyst comprises (1) about 0.5 to 20 weight percent, calculated as weight iodide and based on the total weight of the catalyst of at least one quaternary ammonium or phosphonium iodide, (2) about 0.02 to 20.0 weight percent, based on the total weight of the catalyst, of an organotin (IV) halide containing about 3 to 24 carbon atoms and having the formula

    (R.sup.7).sub.n --Sn--I.sub.(4-n)

wherein each R⁷ substituent independently is selected from alkyl of up to about 12 carbon atoms, benzyl, phenyl or phenyl substituted with up to 3 substituents selected from lower alkyl, lower alkoxy or halogen; and n is 2 or 3; and (3) an essentially non-acidic catalyst support material.
 24. Process according to claim 22 wherein the catalyst comprises a melt of (1) at least one quaternary ammonium or phosphonium iodide, (2) at least one organotin (IV) halide containing about 3 to 24 carbon atoms and having the formula

    (R.sup.7).sub.n --Sn--I.sub.(4-n)

wherein each R⁷ substituent independently is selected from alkyl of up to about 12 carbon atoms, benzyl, phenyl or phenyl substituted with up to 3 substituents selected from lower alkyl, lower alkoxy or halogen; and n is 2 or 3; wherein the weight ratio of (1):(2) is about 1:100 to 50:1.
 25. Process for the isomerization of 3,4-epoxy-1-butene to 2,5-dihydrofuran which comprises contacting 3,4-epoxy-1-butene in the gas phase at a temperature of about 100° to 200° C. and a pressure of about 1.1 to 20 bar with a catalytic amount of a catalyst comprising (1) one or more quaternary ammonium iodides having the formula ##STR29## wherein each R⁵ substituent is independently selected from alkyl of up to 20 carbon atoms and the quaternary ammonium iodide contains about 16 to 60 carbon atoms; and (2) an organotin (IV) compound containing about 3 to 24 carbon atoms and having the formula

    (R.sup.7).sub.n --Sn--I.sub.(4-n)

wherein each R⁷ substituent independently is selected from alkyl of up to about 12 carbon atoms, benzyl, phenyl or phenyl substituted with up to 3 substituents selected from lower alkyl, lower alkoxy or halogen; and n is 2 or
 3. 26. Process according to claim 25 for the isomerization of 3,4-epoxy-1-butene to 2,5-dihydrofuran which comprises contacting the 3,4-epoxy-1.butene in the gas phase at a temperature of about 100 to 200° C and a pressure of about 1.1 to 20 bar with a catalytic amount of a catalyst comprising (1) about 0.5 to 20 weight percent, calculated as weight iodide and based on the total weight of the catalyst, of one or more quaternary ammonium iodides having the formula ##STR30## wherein each R⁵ substituent is independently selected from alkyl of up to 20 carbon atoms and the quaternary ammonium iodide contains about 16 to 60 carbon atoms, (2) about 0.02 to 20.0 weight percent, based on the total weight of the catalyst, of an organotin (IV) compound containing about 3 to 24 carbon atoms and having the formula

    (R.sup.7).sub.n --Sn--I.sub.(4-n)

wherein each R⁷ substituent independently is selected from alkyl of up to about 12 carbon atoms, benzyl, phenyl or phenyl substituted with up to 3 substituents selected from lower alkyl, lower alkoxy or halogen; and n is 2 or 3;and (3) an essentially non-acidic catalyst support.
 27. Process according to claim 25 wherein the catalyst comprises a melt of (1) at least one quaternary ammonium having the formula ##STR31## wherein each R⁵ substituent is independently selected from alkyl of up to 20 carbon atoms and the quaternary ammonium iodide contains about 16 to 60 carbon atoms and (2) at least one organotin (IV) halide containing about 3 to 24 carbon atoms and having the formula

    (R.sup.7).sub.n --Sn--I.sub.(4-n)

wherein each R⁷ substituent independently is selected from alkyl of up to about 12 carbon atoms, benzyl, phenyl or phenyl substituted with up to 3 substituents selected from lower alkyl, lower alkoxy or halogen; and n is 2 or 3;wherein the weight ratio of (1):(2) is about 1:100 to 50:1.
 28. Process for the isomerization of 3,4-epoxy-1-butene to 2,5-dihydrofuran which comprises contacting 3,4-epoxy-1-butene in the gas phase at a temperature of about 100° to 200° C. and a pressure of about 1.1 to 20 bar with a catalytic amount of a catalyst comprising (1) one or more quaternary ammonium iodides having the formula ##STR32## wherein R⁵ is alkyl of up to about 20 carbon atoms and A is the residue of an azabicycloalkane or diazabicycloalkane having 6 to 12 ring carbon atoms; and (2) an organotin (IV) halide containing about 3 to 24 carbon atoms and having the formula

    (R.sup.7).sub.n --Sn--I.sub.(4-n)

wherein each R⁷ substituent independently is selected from alkyl of up to about 12 carbon atoms, benzyl, phenyl or phenyl substituted with up to 3 substituents selected from lower alkyl, lower alkoxy or halogen; and n is 2 or
 3. 29. Process according to claim 28 for the isomerization of 3,4-epoxy-1-butene to 2,5-dihydrofuran which comprises contacting 3,4-epoxy-1-butene in the gas phase at a temperature of about 100° to 200° C. and a pressure of about 1.1 to 20 bar with a catalytic amount of a catalyst comprising (1) about 0.5 to 20 weight percent, calculated as weight iodide and based on the total weight of the catalyst, of one or more quaternary ammonium iodides having the formula ##STR33## wherein R⁵ is alkyl of up to about 20 carbon atoms and A is the residue of an azabicycloalkane or diazabicycloalkane having 6 to 12 ring carbon atoms, (2) about 0.02 to 20.0 weight percent, based on the total weight of the catalyst, of an organotin (IV) halide containing about 3 to 24 carbon atoms and having the formula

    (R.sup.7).sub.n --Sn--I.sub.(4-n)

wherein each R⁷ substituent independently is selected from alkyl of up to about 12 carbon atoms, benzyl, phenyl or phenyl substituted with up to 3 substituents selected from lower alkyl, lower alkoxy or halogen ; and n is 2 or 3; and(3) an essentially non-acidic catalyst support.
 30. Process according to claim 28 wherein the catalyst comprises a melt of (1) one or more quaternary ammonium iodides having the formula ##STR34## wherein R⁵ is alkyl of up to about 20 carbon atoms and A is the residue of an azabicycloalkane or diazabicycloalkane having 6 to 12 ring carbon atoms, (2) about 0.02 to 20.0 weight percent, based on the total weight of the catalyst, of an organotin (IV) halide containing about 3 to 24 carbon atoms and having the formula

    (R.sup.7).sub.n --Sn--I.sub.(4-n)

wherein each R⁷ substituent independently is selected from alkyl of up to about 12 carbon atoms, benzyl, phenyl or phenyl substituted with up to 3 substituents selected from lower alkyl, lower alkoxy or halogen; and n is 2 or 3;wherein the weight ratio of (1):(2) is about 1:100 to 50:1.
 31. Process for the isomerization of 3,4-epoxy-1-butene to 2,5-dihydrofuran which comprises contacting 3,4-epoxy-1-butene in the gas phase at a temperature of about 100° to 200° C. and a pressure of about 1.1 to 20 bar with a catalytic amount of a catalyst comprising (1) one or more quaternary phosphonium iodides having the formula ##STR35## wherein each R⁶ substituent is independently selected from alkyl of up to 20 carbon atoms, benzyl, phenyl or phenyl substituted with up to 3 substituents selected from lower alkyl, lower alkoxy and halogen and the phosphonium iodide contains about 16 to 60 carbon atoms; and (2) an organo tin (IV) halide containing about 3 to 24 carbon atoms and having the formula

    (R.sup.7).sub.n --S--I.sub.(4-n)

wherein each R⁷ substituent independently is selected from alkyl of up to about 12 carbon atoms, benzyl, phenyl or phenyl substituted with up to 3 substituents selected from lower alkyl, lower alkoxy or halogen; and n is 2 or
 3. 32. Process according to claim 31 for the isomerization of 3,4-epoxy-1-butene to 2,5-dihydrofuran which comprises contacting 3,4-epoxy-1-butene in the gas phase at a temperature of about 100° to 200° C. and a pressure of about 1.1 to 20 bar with a catalytic amount of a catalyst comprising (1) about 0.5 to 20 weight percent, calculated as weight iodide and based on the total weight of the catalyst, of one or more quaternary phosphonium iodides having the formula ##STR36## wherein each R⁶ substituent is independently selected from alkyl of up to 20 carbon atoms, benzyl, phenyl or phenyl substituted with up to 3 substituents selected from lower alkyl, lower alkoxy and halogen and the phosphonium iodide contains about 16 to 60 carbon atoms; (2) about 0.02 to 20.0 weight percent, based on the total weight of the catalyst, of an organotin (IV) halide containing about 3 to 24 carbon atoms and having the formula

    (R.sup.7).sub.n --Sn--I.sub.(4-n)

wherein each R⁷ substituent independently is selected from alkyl of up to about 12 carbon atoms, benzyl, phenyl or phenyl substituted with up to 3 substituents selected from lower alkyl, lower alkoxy or halogen; and n is 2 or 3; and(3) an essentially non-acidic catalyst support.
 33. Process according to claim 31 wherein the catalyst comprises a melt of (1) one or more quaternary phosphonium iodides having the formula ##STR37## wherein each R⁶ substituent is independently selected from alkyl of up to 20 carbon atoms, benzyl, phenyl or phenyl substituted with up to 3 substituents selected from lower alkyl, lower alkoxy and halogen and the phosphonium iodide contains about 16 to 60 carbon atoms; (2) an organotin (IV) halide containing about 3 to 24 carbon atoms and having the formula

    (R.sup.7).sub.n --Sn--I.sub.(4-n)

wherein each R⁷ substituent independently is selected from alkyl of up to about 12 carbon atoms, benzyl, phenyl or phenyl substituted with up to 3 substituents selected from lower alkyl, lower alkoxy or halogen; and n is 2 or 3;wherein the weight ratio of (1):(2) is about 1:100 to 50:1. 